On fair weather days, the Toronto SkyDome can do something no other domed stadium in the world can: open its roof completely. Constructed in 1989, the SkyDome is the first and only stadium to have a fully retractable roof. Unlike any other sports stadium, the roof of the SkyDome separates into pieces and disappears from sight in less than 20 minutes, completely uncovering the playing field and more than 91 percent of the seats. How does it work?

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The roof is made of four massive steel panels; one panel is fixed, and the other three slide on a system of steel tracks. Each panel is made from a pattern of steel trusses with a corrugated steel shell and a weatherproof plastic membrane. Opening the roof requires that two panels slide over each other and under a fixed panel behind center field. A third panel, which starts behind home plate, rotates on a circular rail. Despite its enormous weight -- the whole roof weighs more than 11,000 tons -- the roof panels slide at a whopping rate of 71 feet per minute!

Today, the SkyDome is home to the American League's Toronto Blue Jays and the Canadian Football League's Toronto Argonauts. The retractable roof was closed twice in the Blue Jays' first year in the dome and has closed four or five times a year since then.

Here's how this dome stacks up against some of the biggest domes in the world.
(diameter, in feet)

SkyDome674'

Fast Facts:

The SkyDome JumboTron is a 115-foot-by-33-foot video display board that has 420,000 light bulbs, making it the largest scoreboard in the world.

A 348-room hotel is located in center field. Seventy of those rooms have views of the field.

When the roof is open, the closed end of the stadium causes a downdraft in the outfield that tends to prevent home runs.